Cement structures in wellbores such as cement sheaths and cement plugs, can be damaged resulting in failures i.e. micro-annuli, cracks, and other voids, in the cement.
A number of ways are currently used to repair these failures. Micro-cement systems such as SqueezeCRETET™ (Schlumberger) are used to repair cracks and other voids in cement sheaths. These formulations are able to penetrate cracks with widths down to about 120 microns. However the size and concentration of the micro-cement particles do not allow penetration into cracks of smaller size. Nano-sized based sealants have improved penetration (EP application no. 07119640.6) compared with micro-cement based sealing technologies but it is difficult to retard the setting reaction. Alkali swellable latex (ASL) solutions also have better penetration than micro-cement systems and will set only in contact with the cement (or other high pH source). However the long term durability of the ASL solutions have not been established.
WO 00/66878 discloses a sealing material made by combining an oxide or hydroxide and a phosphate with water to form a slurry which cures to form a high strength, minimally porous material which binds to underground formations, steel and ceramics. However, this material contains solids such as fly ash or insolubles oxide which reduce the injectivity; moreover the material sets on his own which requires more engineering work in order to make sure that the sealing material is liquid during a long enough period of time to be pumped but then should set in a reduced period of time for being industrially interesting.
US 2006/086501 describes a sealant composition comprising a swelling agent to maintain isolation of the formation, or reduce fluid loss in a well bore. In this patent application the swelling agent is a swelling polymer that swells when in contact with water.
The current invention aims to avoid the disadvantages of previous solutions by providing a solids-free repair fluid that can penetrate small gaps in cement structures of wellbores and for which the resultant solid formed are known to have long term durability.